Roll-forming of transition surfaces on cylindrically shanked element

ABSTRACT

A method for forming transition surfaces to close tolerances, with cold worked properties, and with improved surface finish from the self-material of a circularly cylindrical shanked metallic workpiece. In the process, the workpiece is forced endwise against a forming surface on a roll die while the roll die is pressed radially against the workpiece. The resulting displacement of metal serves to work harden the transition surface, smooth it to the surface quality of the die itself, and hold its dimensions to the close tolerances required of the product. If desired, the transition surface can be formed as a peripheral bead, and its trailing surface formed as a consequence of springback forces in the material.

United States Patent Duncan et al.

451 Jan. 25, 1972 L. F. Kau, Redondo Beach; Lawrence H. Livennont, Glendora, all of Calif.

Assignee: Iii-Shear Corporation, Torrance, Calif.

Filed: Feb. 2, 1970 Appl. No.: 7,459

US. Cl ..72/100, 72/109, 72/111 Int. Cl. ....B2lh l/00, B2lh 3/02 Field of Search 2/80, 84, 102, 103, 104, 107,

References Cited UNITED STATES PATENTS 3/1941 Lauer 72/100 Primary ExaminerLowell A. Larson Attorney-Angus and Mon [5 7] ABSTRACT A method for forming transition surfaces to close tolerances, with cold worked properties, and with improved surface finish from the self-material of a circularly cylindrical shanked metallic workpiece. 1n the process, the workpiece is forced endwise against a forming surface on a roll die while the roll die is pressed radially against the workpiece. The resulting displacement of metal serves to work harden the transition surface, smooth it to the surface quality of the die itself, and hold its dimensions to the close tolerances required of the product. If desired, the transition surface can be formed as a peripheral bead, and its trailing surface formed as a consequence of springback forces in the material.

5 Claims, 7 Drawing Figures PATENIED JAN25 I972 WILLIAM E. DUNCAN, HARRY LE KAU,

MWRE/VCE H. L/VfRMONT INVENTORS I A TTOR/VEKi.

ROLL-FORMING F TRANSITION SURFACES 0N CYLINDRICALLY SHANKED ELEMENT This invention relates to the formation of transition surfaces to very close tolerances on circularly cylindrically metallic objects, and with improved surface finish, and with hardness developed by cold working.

It is common practice to force an oversize fastener pin into an undersize hole for the purpose of providing a tight fit between them. This is called an interference fit. A threaded pin used for such an installation is proportioned such that its threads pass freely through the hole so as not to spoil them. However, there must be a transition section which contacts the wall of the hole and expands it to the size of the shank. This is a critical section because the localized forces on it are quite severe. A soft transition section will become severely galled, so it should be hardened preferably by cold working. Surface roughness will cause difficulties and uncertainties in the insertion, so it should be smooth, and because it serves to displace material forming the hole wall, its dimension must be closely controlled.

For example, there exists in the fastening field a fastener known as the l-li-Tigue" which includes a fastener shank having a shank and an adjacent peripheral sloping surface and enlargement (together comprising the transition surface) involving some closely controlled dimensional relationships relative to the pin and to the wall of the hole into which it is to be inserted. The purpose of the enlargement is to coldwork the wall of the hole as it passes therethrough, and to provide for improved joint characteristics. This device is shown in the presently copending United States patent application of Leonard A. I-Iarvill and William E. Duncan, Ser. No. 857,293, filed Sept. 3, 1969, and entitled Fastener Including Expander Means and Joint Including the Same" (now US. Pat. No. 3,578,367, issued May 11, 1971) assigned to the same assignee as the instant patent application, to which reference may be made for a more complete exposition of the device.

The transition surface which is the subject of that patent application is very carefully controlled as to dimensions relative to the cylindrical shank, and involves a differential diameter relative to its shank of the order between about 0.00070.00l0 inches. The length of the enlargement varies within a range of about 0.550-0070 inches, and these foregoing close dimensions are formed on fasteners having a nominal diameter in the range of between about l/32-9/l6 inches. Evidently these enlargements must be formed on bodies which have tolerances involved in their cylindrical shanks so that the close control of the differential diameter becomes a critical and difficult matter to control and yet this difference must be very carefully controlled if the device is to be useful for its intended function. In simpler devices, a sloping surface may be provided on the shank to provide at least some of the advantages of the more complicated pin, but its dimensions and shape are as critical. It is an object of this invention to provide a method for forming transition surfaces to close tolerances by means of a die-rolling technique, and with good surface smoothness and hardness.

A process according to the present invention includes the utilization of a rolling die which has a peripheral cavity with a greater and lesser projecting diameter, and between them a forming cavity. The blank upon which the operation is conducted has a cylindrical shank nominally equal to the desired final shank diameter and a tapering step upon which the die is to work.

According to the invention, the roller die is brought against the object, with the forming surface bearingagainst it in the region of the tapering surface. With the roll die and the workpiece tuming, radial force is exerted against the roll die to force it against the workpiece and an axial endwise force is brought against the workpiece to force it against the roll die thereby to displace metal and form the transition surface.

The transition surface is then closely related to the shank diameter, and its shape is defined by the die. Furthermore it is cold worked and smooth.

According to a preferred but optional feature of the invention, the forces on the roll die and workpiece are coordinated, and brought to a desired level, which is indicative of the displacement of sufficient metal to complete the transition surface and upset material to form an enlarged peripheral bead. After sufficient revolutions have occurred to form what will become the leading surface of the bead, the endwise pressure is released, and springback of the material related to the die will cause a portion of the upset material to work against a reentrant portion of a peripheral wall forming a cavity in the die and form at least a part of the reverse side of the bead. At the same time a region of lesser diameter of the die will have borne against the shank so as to provide a reference relative to which the bead is formed, whereby the necessary close diametral relationship of the shank and of the bead is established by the roll die.

The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings in which:

FIG. I is a side view of a workpiece to be formed according to the invention;

FIGS. 2, 3, and 4 show sequential steps in the conduct of one embodiment of the invention;

FIG. 5 shows the completed device produced in FIGS. 2-4, after a further step;

FIG. 6 is'a view principally in schematic notation showing machinery for conducting the process according to the inven tion; and

FIG. 7 shows another embodiment of the invention.

In FIG. I there is, shown a blank 10 which is the workpiece to be worked upon in both embodiments of the instant invention. This blank includes a head 11 shown as a countersink head but which may be of any other desired shape instead, a cylindrical shank portion 12, a taper portion 13 contiguous to the shank portion, a thread portion 14, and a chamber 15. The blank has a central axis 16.

One object of this invention, and exemplifying the presently preferred embodiment of the method, is to form the transition surface on fastener pin 20 shown in FIG. 5. In this case an external thread 21 has been formed on thread portion 14 by rolling operations which do not form part of the present invention. The present invention is intended to form sloping surface 21a and bead 22 (together being sometimes called a transition surface). The bead is shown as an enlargement with a maximum diameter K. The shank has a diameter D, and the bead is contiguous to it. The control of the dimension K-D is critical in this invention and permits only the very narrowest of tolerances, tolerances so narrow that they have not heretofore been possible to secure in practical die rolling operations because of the inherent variations in the diameter of the workpiece itself.

Dimension M indicates the length of the bead, and as stated above, the general dimensions of this bead in the fastener shank size range between about If 32 and 9/16 inches is on the order of the following: K-D: 0.0007-0.00l0, and M: 0.055-0.070 These dimensions are in inches.

In use, this fastener pin is forced through a hole having an initial diameter less than that of diameter D. The sloping surface and bead cause a local temporary enlargement of the wall of the hole thereby coldworking the wall surface which thereafter shrinks upon the shank to form an interference it. The localized forces are quite large, and cold-worked hardness greatly improves the integrity of the pin. The improved smoothness creates better burnishing of the wall of the hole. The wall of the hole is burnished by the insertion of the pin, and the joint has improved fatigue-resisting properties. A threaded collar is attached to thread 21.

The bead and the sloping surface are rolled according to this invention by the use of mechanism schematically shown in FIG. 6. In this mechanism, a pair of roll dies 25, 26 are mounted for powered rotation on their centers as indicated. The center of roll 26 may be mounted on a rigid mount, and need not be laterally movable, although it could be. A support blade 27 supports the workpiece which is to be worked upon, and roll is supported by a mount 28 which is radially movable relative to the center of rotation. This mount and thereby the roll die is movable by first motor means 29 such as a fluid motor, a piston and cylinder being a suitable example. A pressure gauge 30 is provided for purposes yet to be discussed. This motor receives its power from a power source 31 such as a pump or other source through a three-way valve 32 which has the function of alternatively connecting the power source to the motor or of venting the motor to a vent 33. It will be seen that when the pressure is on in the line 34 to the first motor means, a workpiece resting on the blade will be compressed between the two roll dies by virtue of the radial force exerted by the motor means, and with a force proportional to the pressure indicated by gauge 30.

End thrust means 35 is provided for exerting an endwise load on the fastener. This conveniently comprises second motor means 36 which presses directly upon the headed end of the blank. Again there are a power source 37, and a threeway valve 38 adapted to alternately connect line 39, and thereby the motor means, to the-power source or to vent 40. A pressure gauge 41 is provided to determine pressure in the motor and thereby the force being exerted against the end of the workpiece, to provide stopping of the forming action when the surface is fully formed. This compensates for variations in the length of the part. Similar force determination can be made in the radial feed of die 25 to determine and stop fonning when the die 25 contacts shank 12 to compensate for shank. diameter variations.

In both circuits, pressure gauges 30 and 41 are force-sensing means intended to disclose to the operator whether a given force relationship exists between the workpiece and the dies whereby to indicate whether or not an adequate movement of material has occurred to create the proper head. The roll dies are conventionally generally cylindrical, and have respective parallel axes of rotation 45.

In FIGS. 24, only the cross section of the fonning regions are shown, it being understood that the cross sections shown represent a structure which extends peripherally and uniformly around the roll die. Roll die 25 is shown and described in detail, it being understood that roll die 26 is identical to it.

' Roll die 25 has .a first diameter 46 and a second diameter 47, diameter 47 being the greater. Surface 48 is cylindrical and corresponds to diameter 46. The shape of surface 49 corresponding to diameter 47 is arbitrary although it will customarily be made of cylindrical shape. It is not used in the forming process. However, surface 48 aids in determining the relationship between diameters K and D because it rolls along the surface of the shank.

A bead-forming cavity 50 is formed between the two surfaces 48 and 49. It includes a first, leading, forming surface 51 which in use faces toward the headed end of the fastener and extends down to diameter 47 and upwardly to a distance such that its difference from diameter 46 will be the'desired value of K minus D, plus allowance for springback of the material after the forming forces are removed. It forms sloping surface 210 and the leading part of bead 22. The dimensions of the die will not correspond exactly to the ultimate shape of the surfaces formed because of the springback forces involved. Nevertheless the differences are quite small and the considerations in relating them are well known in the die making trade.

Surface 51 extends and blends into a second, trailing fonning surface 52 which is contiguous to surface 51 and reentrant in the sense that it reverses the direction of the roll-forming cavity and begins to taper toward diameter 46. The length of this forming surface 52 which is used is frequently less than the full distance out to surface 48, but the exact length used is somewhat indeterminate for reasons to be disclosed. The surface 52 is utilized to form part of the trailing surface of the bead.

In the course of the process, the dies are brought against the workpiece by actuation of three-way valve 32 to apply pressure to the roll-form dies. It will be noted that at this time there is contact between the taper portion and the forming surfaces. Thereafter, as shown in FIG. 3 an endwise force exemplified by arrow 53 is applied to the headed end of the fastener. This is accomplished by setting three-way valve 38 so as to apply power to the second motor means 36. Now pressure will begin to build up in both of the circuits and it will do so as a direct result of the endwise force applied in a forming manner as shown in FIG. 3.

There is a wave 55 of material displaced axially and reacting radially as a consequence of the contact between the taper portion 13 and forming surface 51. This motion results in cold working of the transition surface. Of course the smoothness corresponds to that of the die. It will be noted that the beadforming cavity is not necessarily filled, and that there is a region 56 on the fastener which is indeterminately formed because there has been no contact with the die. The machinery may be automated for correlating the pressures sensed by gauges 30 and 41 or the gauges may simply be watched by the operator, and the machine controlled manually, and when they have reached values which must be determined from machine to machine and part to part, but which are repetitive once established, which are found by adjustment and trial and error to have formed the forward portion to adequate tolerances then, three-way valve 38 is turned so as to vent the second motor means and relieve the end pressure on the fastener. Speaking generally, it is desired to fill about 75 percent of the volume of the recess in FIG. 3.

Therelief of the endwise force results in a springback force shown by arrow 57 in FIG. 4, derived from the pressure still maintained on in the circuit leading to first motor means 29 causing the shank to react against the leading forming surface 51. This causes that portion of the indeterminate region 56 which is contiguous to surface 52 to be formed in a reentrant manner so that a portion 58 of the back face 59 of the bead is worked and brought to its desired shape.

FIG. 7 illustrates a variation of the foregoing. It differs from it in that no bead is formed, but instead the cavity forms only sloping surface 65. The workpiece of FIG. I is used to produce fastener 66, and the same class of roll die is used. It will be noted that roll die has a pair of diameters 67, 68 extending to first (cylindrical) surface 69 and second surface. 70. The recess 71 has a leading forming surface 72 which fairs into surface 69. This roll die therefore displaces material to form transition surface 65, and rolls its outer diameter to that of shank 73. However, the same rolling technique is used as in FIGS. 2-4, except that the release of the endwise force is not performed to roll a surface, but only to release the workpiece.

It will thereby be seen that this rolling technique, comprising a primary endwise loading, a secondary release of the same while the workpiece remains in contact with the roller dies (while making the device of FIG. 5) will have worked the leading, and in making the device of FIG. 5 part of the trailing, edge of the transition surface. It will be found that when portion 58 is worked the remainder 59 of the transition surface between the bead and the shank will be of suitable shape and structure for the intended use of the device.

I will also be noted that in the device of FIG. 5 the dimension K-D has been closely formed to exact dimensions because of the relationship of the contact of surface 48 with the shank, and of the wave of material with the deepest portion of the bead-forming cavity. The same result obtains in FIG. 7, except that the sizing of the maximum diameter is that of the shank rather than that of an enlarged bead.

The foregoing results will not be obtained, however, unless there is an adequate volume of metal moved to fill the cavity beyond its deepest point.

With such small dimensions as are involved in K-D (or equality of K and D in FIG. 7) and with the tolerances which appear on even very carefully ground workpieces, dimensional limit stops and the like are not suitable for controlling this process. Therefore the force controls heretofore described are used instead, and it will be found that there is a direct relationship between the pressure (force) readings on the two force-measuring devices and the displacement of an adequate of material to create the desired beads. In fact, these pressure readings can be utilized as inspection means. Because an out-of-tolerance shank cannot be used to form a proper bead, sufficient material is unlikely to be displaced to cause the resultant force. For example, if an insufficient pressure were developed in pressure gauge 30 regardless of the reading on gauge 41, it could be concluded that there was never sufficient resistance at the die to represent movement of an adequate volume of metal and the device would be rejected. The system shown in FIG. 6 may of course be operated manually by an individual observing the dial readings. Its automation is obvious and forms no part of this invention.

There is thereby provided a technique for roll-forming a transition surface on a metal workpiece, and if desired for utilizing force relationships as a control over the system, and axial springback to machine a back surface of a bead in order to provide a optimum structure.

This invention is not to be limited by the embodiments shown in the drawings and described in description which are given by way of example and not of limitation but only in accordance with the scope of the appended claims.

We claim:

1. A method for rolling a transition surface from the self material of a metallic blank requiring the movement of metal, said blank having a central axis and an initial configuration which includes a cylindrical shank portion and a contiguous taper portion which decreases in diameter as it extends away from the shank portion, the portions being surfaces of revolution concentric around said central axis, and using a roll die with a circular periphery including a cylindrical first surface with a first diameter, an axially spaced apart second surface with a second, larger, diameter, and between them forming a cavity in the form of a peripheral groove bounded adjacent to the said second surface by a leading forming surface extending from the second diameter to a diameter at least as great as that of the first diameter as said leading forming surface extends toward said first surface, said method comprising the following steps in the order recited:

a. bringing the first surface of the roll die against the cylindrical shank portion and turning the blank and the die around their axes;

b. exerting an endwise force upon the blank to press the taper portion against the leading forming surface while maintaining the roll die pressed radially against the blank thereby to form a wave of material on the blank in contact with the said leading forming surface, and maintaining the endwise and radial forces and rotation of die and blank until the wave has extended to the full extent of the leading forming surface, in order to form the transition surface, cold work the metal, and form and smooth the same.

2. A method for rolling a transition surface which includes a projecting peripheral bead from the self material of a metallic blank having a central axis and an initial configuration which includes a cylindrical shank portion and a contiguous taper portion which decreases in diameter as it extends away from the shank portion, the portions being surfaces of revolution concentric around said central axis, and using a roll die with a circular periphery including a cylindrical first surface with a first diameter, an axially spaced apart second surface with a second, larger, diameter, and between them a bead forming cavity in the form of a peripheral groove bounded adjacent to the said second surface by a leading forming surface extending from the second diameter to a diameter less than that of the first diameter as said leading forming surface extends toward said first surface, and a trailing forming surface adjacent to the leading fonning surface increasing in diameter as it extends toward the said first surface, said method comprising the following steps in the order recited:

a. bringing the first surface of the roll die against the cylindrical shank portion and turning the blank and the die around their axes;

b. exerting an endwise force upon the blank to press the taper portion against the leading forming surface while maintaining the roll die radially pressed against the blank thereby to form a wave of material on the blank in contact with the said leading forming surface, and maintaining the endwise and radial forces and rotation of die and blank until the wave has extended to the full extent of the leading forming surface; and

c. thereafter releasing the endwise force while maintaining the rotation and radial force on the roll die whereby springback of the material, while the blank remains in contact with the leading forming surface, causes formation of at least part of the wave by contact with at least that part of the trailing forming surface which is closest to the leading forming edge.

3. A method according to claim 2 in which force sensitive means is provided for indicating the force which is radially pressing the roll die against the workpiece, and the endwise force, and maintaining both forces until a predetermined value of both is reached in step (b) prior to accomplishing step (c).

4. A method according to claim 3 in which both of the forces are maintained until the wave of material has passed the leading forming surface.

5. A method according to claim 2 in which a pair of said roll dies is provided, the rolls being on diametrically opposite sides of the blank.

CERTIFICATE ore-oP t-matrim Patent No.

3,636,746 Dated January 25, 1972 Inventor-(s) Duncan et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 4, 'cylimilrically" should read --c lindrical-- trolled-- line 43, "0.550" should read --0.055- Col. 2, line 36, "chamber" should read --chamferline 57 after "0.070' insert a period line 62, "it" should read "fit- Col. 4', line 61, "I" should read --11;-- Col. 5, line 5, after "adequate" insert quantity-- line 2l, "a" should read -an-- I Signed and sealed this 8th day of October 1974,

(SEAL) Attest: v

McCQY M. GIBSON JR. c. MARSHALL DAWN Attesting Officer Commissioner of Patents r- ORM PO 1050 (1 9) uscoMM-Dc oos'ls-Pos 0.5. GOVERHMIN'I HUNTING OFFICE IIED 0-S0-IS line 25, closely controlled" should read --closelycon- 

1. A method for rolling a transition surface from the self material of a metallic blank requiring the movement of metal, said blank having a central axis and an initial configuration which includes a cylindrical shank portion and a contiguous taper portion which decreases in diameter as iT extends away from the shank portion, the portions being surfaces of revolution concentric around said central axis, and using a roll die with a circular periphery including a cylindrical first surface with a first diameter, an axially spaced apart second surface with a second, larger, diameter, and between them forming a cavity in the form of a peripheral groove bounded adjacent to the said second surface by a leading forming surface extending from the second diameter to a diameter at least as great as that of the first diameter as said leading forming surface extends toward said first surface, said method comprising the following steps in the order recited: a. bringing the first surface of the roll die against the cylindrical shank portion and turning the blank and the die around their axes; b. exerting an endwise force upon the blank to press the taper portion against the leading forming surface while maintaining the roll die pressed radially against the blank thereby to form a wave of material on the blank in contact with the said leading forming surface, and maintaining the endwise and radial forces and rotation of die and blank until the wave has extended to the full extent of the leading forming surface, in order to form the transition surface, cold work the metal, and form and smooth the same.
 2. A method for rolling a transition surface which includes a projecting peripheral bead from the self material of a metallic blank having a central axis and an initial configuration which includes a cylindrical shank portion and a contiguous taper portion which decreases in diameter as it extends away from the shank portion, the portions being surfaces of revolution concentric around said central axis, and using a roll die with a circular periphery including a cylindrical first surface with a first diameter, an axially spaced apart second surface with a second, larger, diameter, and between them a bead forming cavity in the form of a peripheral groove bounded adjacent to the said second surface by a leading forming surface extending from the second diameter to a diameter less than that of the first diameter as said leading forming surface extends toward said first surface, and a trailing forming surface adjacent to the leading forming surface increasing in diameter as it extends toward the said first surface, said method comprising the following steps in the order recited: a. bringing the first surface of the roll die against the cylindrical shank portion and turning the blank and the die around their axes; b. exerting an endwise force upon the blank to press the taper portion against the leading forming surface while maintaining the roll die radially pressed against the blank thereby to form a wave of material on the blank in contact with the said leading forming surface, and maintaining the endwise and radial forces and rotation of die and blank until the wave has extended to the full extent of the leading forming surface; and c. thereafter releasing the endwise force while maintaining the rotation and radial force on the roll die whereby springback of the material, while the blank remains in contact with the leading forming surface, causes formation of at least part of the wave by contact with at least that part of the trailing forming surface which is closest to the leading forming edge.
 3. A method according to claim 2 in which force sensitive means is provided for indicating the force which is radially pressing the roll die against the workpiece, and the endwise force, and maintaining both forces until a predetermined value of both is reached in step (b) prior to accomplishing step (c).
 4. A method according to claim 3 in which both of the forces are maintained until the wave of material has passed the leading forming surface.
 5. A method according to claim 2 in which a pair of said roll dies is provided, the rolls being on diametrically opposite sides of the blank. 